Rates, catalysts and reliable endpoints
도입됨| English | 의미 |
|---|---|
| rate/reɪt/ | 반응 속도 |
| activation energy/ˌæktɪˈveɪʃn ˈenədʒi/ | 활성화 에너지 |
What would explain this observation?
- A faster reaction finishes sooner, but it need not make more product. Rate 速率 and final yield answer different questions.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Reaction rate describes reactant used or product formed per time. Higher temperature increases the fraction of collisions with enough energy. A catalyst provides an alternative pathway with lower activation energy 活化能.
- activation energy: The minimum energy that particles must have for a reaction to occur; rate: Change in a measured quantity per unit time.
Two reactions reach the same final gas volume. Which can still differ?
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
The final volume depends on the amounts reacting, not on how fast they react. Two reactions with the same amounts reach the same final volume even if one is much faster; rate is about time, not about the balanced totals.
Match each technical term to its precise meaning.
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A product-time graph has a steeper gradient where rate is larger. A tangent estimates instantaneous rate; a secant gives average rate over an interval. The final plateau reflects the total collected product under the stated conditions.
- For gas production, check apparatus for leaks, start timing consistently and record volume at regular intervals. Keep concentration, reactant amount and surface area controlled when changing temperature.
Which two habits make the investigation or model in this case more defensible?
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: gas volume increases from 10 to 34 cubic centimetres between 20 and 60 s. Average rate = change in volume/change in time. Rate = (34 - 10)/(60 - 20) = 0.60 cubic centimetres per second. This is not necessarily the instantaneous rate at 40 s.
A reaction makes 24 cubic centimetres of gas in 40 s. Find average rate. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A reaction makes 24 cubic centimetres of gas in 40 s. Find average rate.
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
The result is 0.6 cm³/s. Known: 24 cubic centimetres of gas in 40 s. Use average rate = volume / time. Rate = 24/40 = 0.6 cubic centimetres per second. This average over the interval need not equal the instantaneous rate at any moment.
Check the conclusion and its limits
- A catalyst does not change the final equilibrium composition at fixed conditions. A mass-loss method cannot detect all reactions, and losing gas through a leak biases a collection experiment.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A faster reaction always produces a larger final amount of product. This claim is false: Rate measures how quickly product forms, not how much finally forms. The final amount is fixed by the limiting reagent; a catalyst or powder changes only the time taken to reach it.
Rates, catalysts and reliable endpoints: A product-time graph has a steeper gradient where rate is larger. A tangent estimates instantaneous rate; a secant gives average rate over an interval. The final plateau reflects the total collected product under the stated conditions.
A faster reaction always produces a larger final amount of product.
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
Rate measures how quickly product forms, not how much finally forms. The final amount is fixed by the limiting reagent; a catalyst or powder changes only the time taken to reach it.
The minimum energy that particles must have for a reaction to occur: write the technical term.
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
activation energy means The minimum energy that particles must have for a reaction to occur.